The present invention relates to a method and apparatus for delivering an aerosol, nebulized liquid, solid medicine or a vapor to a patient""s respiratory tract. More particularly, the present invention relates to a breath actuated nebulizer with reduced resistance to a patient""s inhalation.
Medical nebulizers that generate a fine spray or nebula of a liquid medicine for inhalation by a patient are well-known devices commonly used for the treatment of certain conditions and diseases. Nebulizers have applications for conscious, spontaneously-breathing patients and for controlled, ventilated patients.
In some nebulizers, a gas and a liquid are mixed together and directed against a baffle. As a result, the liquid is aerosolized, that is, the liquid is caused to form small particles that are suspended in the air. This aerosol of the liquid can then be inhaled into a patient""s respiratory tract. One way to mix the gas and liquid together in a nebulizer is to pass a quickly moving gas over a liquid orifice tip of a tube. A negative pressure created by the flow of pressurized gas is a factor that contributes to drawing liquid out of the liquid orifice into the stream of gas and nebulizing it.
Important considerations in the design of a nebulizer are the timing and dosage regulation of the aerosolized medication. In some nebulizer designs, a continuous stream of pressurized gas entrains the liquid against the baffle to constantly generate aerosol particles until the liquid in a reservoir is depleted. Continuous nebulization may result in a waste of aerosol during a patient""s exhalation or during a delay between inhalation and exhalation. The amount of wasted aerosol may be difficult to quantify and some medication may be lost to condensation on the nebulizer or mouthpiece during periods of non-inhalation. Nebulizers implementing a timed or non-continuous nebulization may adversely affect particle size and density as the nebulization is turned on and off.
Effective and economical nebulizer therapy includes the ability to quickly generate a large amount of aerosol within a predetermined particle size range. An effective nebulizer preferably provides these features synchronously with the inhalation of the patient. Additionally, it is desirable that a nebulizer have adequate sensitivity to quickly respond to an inhalation while not adversely restricting the patient""s inhalation. Further, an indication that the nebulizer is responding to the patient""s inhalation would be useful.
Accordingly, there is a need for an improved nebulizer having these characteristics.
According to a first aspect of the invention, a nebulizer is provided having a housing with a chamber for holding an aerosol. An air outlet is connected to the chamber permitting the aerosol to be withdrawn from the chamber. A liquid orifice communicates with the chamber. A pressurized gas inlet is positioned adjacent the liquid orifice and is also in communication with the chamber. A diverter movably positioned in the chamber and relative to the air inlet and liquid orifice is designed to divert pressurized gas from the inlet and over the liquid orifice when the diverter is in a nebulizing position. A valve assembly comprising an actuator piston and a relief piston are positioned in the chamber. The actuator piston is connected to the diverter and responsive to inhalation through the air outlet so that the diverter quickly moves into the nebulizing position during the beginning of an inhalation. The relief piston is responsive to additional negative pressure in the chamber after the initial period of inhalation and is movable to allow increased air flow into the chamber so that the effort necessary for a patient inhaling through the air outlet is maintained in a desired range. In one preferred embodiment, a nebulization indicator attached to the actuator piston provides a visual cue that nebulization has begun.
According to another aspect of the invention, a method of providing a patient with an aerosol flow of medicine includes the steps of providing a nebulizer having an outlet for delivering of the aerosol to the patient, a chamber, an actuator piston having a diverter mounted in the chamber, and a relief piston connected to the actuator piston and inhaling air from the chamber through the outlet. The actuator piston and diverter move from an initial position to a predetermined distance from a pressurized gas inlet in the chamber. The diverter diverts pressurized gas injected into the chamber and creates a negative pressure over a liquid outlet. The negative pressure draws medication through the liquid outlet and begins nebulization. The relief valve is then opened to permit greater air flow through the chamber after the diverter has moved to the predetermined distance from the pressurized gas inlet and nebulization has begun.